1. Field of the Invention
The present invention relates to an attachment means for facilitating the attachment of a sheet-formed abrasive or polishing means, such as abrasive paper, to a magnetized support, such as a magnetized rotatable supporting plate in an apparatus for performing abrasion and/or polishing.
2. The Prior Art
In the art of materiallography (the study of materials, e.g. metals) it is common practice to grind and/or polish the samples before performing the various analysis on them. For most analysis it is crucial that the surface of the sample to be analyzed is as smooth as possible.
Accordingly a great number of abrasive and polishing means, e.g. in terms of abrasive sheets having various grinding grain sizes are used. The treatment of a materiallographic sample normally starts with an abrasive sheet having a relatively large grain size and eventually ends up with an abrasive sheet having a very small grain size and/or a polishing cloth, the process comprising a number of treatment steps using means each having different and gradually reduced grain sizes. It is therefore crucial that the changing of the abrasive means is as simple and easy as possible. Furthermore it is desirable that the reuse of not completely worn out abrasive means is facilitated.
It is known to provide the back of abrasive paper with an adhesive layer and to attach the abrasive paper to a rotatable supporting plate by means of the adhesive layer.
It is also known to attach sheet-formed abrasive or polishing discs to a rotatable supporting plate by using magnetic force. Such a grinding and polishing machine comprising a rotatable magnetized supporting plate is common in the art of materiallography, and it is thus desirable that any equipment for use in said art is adapted or adaptable for use in such type of machine.
Thus, from U.S. Pat. No. 4,667,447 an abrasive disc is known comprising a plastic basis layer being coated on one side with a layer of abrasive grains and in which ferromagnetic particles are embedded in an amount sufficient for retaining the abrasive disc to a rotatable magnetic supporting plate with sufficient force for the abrasive disc in use hereof whereby the supporting plate is rotated not to be turned in relation to the latter.
According to U.S. Pat. No. 4,667,447 it is inexpedient to replace the plastic basis layer with embedded ferromagnetic particles by a thin metal foil, as the abrasive disc hereby becomes too rigid to be usable for abrading curved plates.
The abrasive discs mentioned in the said U.S. patent may for example be prepared from a conventional abrasive disc by adhering to its back a so-called liner consisting of an abrasive layer and a basis layer containing particles of a ferromagnetic substance.
When using a thus modified abrasive disc it is positioned directly on the rotatable magnetized supporting plate.
It is a significant disadvantage of the known method described above of attaching a sheet-formed abrasive or polishing means to a magnetic support that after wearing-down of the layer of abrasive grains it is necessary to dispose of the entire combination of abrasive disc, adhesive layer and ferromagnetic layer.
Accordingly the said method is both expensive to use and inappropriate from an environmental point of view. It is thus desirable to obtain a method of attaching a conventional abrasive sheet to a magnetized support without the use of excess material which has to be discarded along with abrasive sheet.
Another way of temporarily attaching an abrasive sheet to a rotatable support is disclosed in EP-B1-0 005 161. This document discloses an abrasive sheet having a backside comprising a release layer of polyamide or polyvinyl acetate copolymer material in order to enable an easy removable of the sheet from a support comprising an adhesive.
It is, however, inconvenient to place a layer of adhesive material directly on the magnetized support if the support is still to be used with ordinary magnetic tools. Furthermore, the adhesive material will eventually loose its adhesive effect, and replacement of the entire support or application of a new adhesive layer is both costly and troublesome.
Another disadvantage of having an adhesive layer on the support is that the applied abrasive sheets might not all have exactly the same size. Accordingly if the entire support is coated with an adhesive, and an abrasive sheet smaller than the support is used, some of the adhesive will be exposed to the dust, dirt and optional liquid from the grinding process and thus be adversely effected. On the other hand, if too small a part of the support is covered with adhesive, the adhesive effect might be too small and the abrasive sheet will be displaced or even detached during grinding having potentially even worse consequences.
A further downside of the system according to EP-B1-1 005 161 is that it is inconvenient that only a certain kind of abrasive sheets comprising a special release layer on the backside can be used.
Accordingly it is an objective of the present invention to provide a system which enables and facilitates the attachment and detachment of virtually any common abrasive sheet to a magnetized support in a grinding and/or polishing machine.